Woot via Amazon offers Prime members the refurbished Arris SurfBoard DOCSIS 3.0 Cable Modem, model no. SB6141, for $39.99 with free shipping. (Non-members can spend $49 to qualify for free shipping; otherwise, shipping costs $8.80.) That's a $5 drop from two days ago and the lowest total price we've seen. (It's the best now by $10.) It features support for IPv4 and IPv6 and enhanced network management. Note that it may not be compatible with all service providers.
A 90-day warranty applies, although it's unclear who backs it.